Fibroblasts are best known for their roles in matrix remodeling, which, in pathological states, can result in tissue destruction or fibrosis (16–18). However, in tissues like lymph nodes, fibroblastic stromal cells control T cell responses in the paracortex. Under basal conditions, they produce homeostatic CCL19, CCL21, and IL-7, which support T cell accumulation and survival (19, 20). Then, following activation, they suppress T cell responses via the production of nitric oxide (21–23). In some autoimmune inflammatory disorders such as rheumatoid arthritis (RA), fibroblasts are major producers of IL-6 as well as a range of other cytokines and chemokines (24–26). Thus, a key role for fibroblasts as both drivers and regulators of inflammation in specific tissue sites is emerging. However, the role of fibroblasts in adipose tissue inflammation, glycemic control, and metabolic syndrome is poorly defined. The lack of specific fibroblast markers and selectively expressed regulators of their function have been major challenges in studying and therapeutically targeting fibroblasts. Cadherin-11 is a classical mesenchymal cadherin that mediates the homotypic cell-to-cell adhesion that is important in tissue morphogenesis and architecture (27, 28). Cadherin-11 is expressed by fibroblasts and myofibroblasts in a variety of tissues such as skin, lung, and joint synovium, and its expression can be induced by inflammatory stimulation (18, 29–31). Interestingly, targeting cadherin-11 by genetic deletion or mAb blockade has been shown to abrogate pathological fibroblast behavior in mouse models of destructive inflammatory arthritis and skin and lung fibrosis (18, 29, 30).

Using cadherin-11 as a marker and functional modulator of fibroblasts, we show that fibroblastic stromal cells in adipose tissue regulate macrophage phenotype and glucose intolerance in diet-induced obesity. We found that cadherin-11–deficient mice had increased IL-33–producing PDGFRα+ fibroblasts, increased ILC2s and IL-13, and an associated expansion of M2 macrophages. Reduced adipose tissue inflammation in cadherin-11–deficient mice was associated with improved glycemic control and metabolic syndrome. Similar findings were noted after anti–cadherin-11 mAb therapy in WT mice.

Cadherin-11 is expressed by fibroblasts in adipose tissue. Adipocytes can be separated from the stromal vascular fraction (SVF) cells that contain the leukocytes and stromal cells after enzymatic digestion of adipose tissue. Surface expression of cadherin-11 was detected by flow cytometry on nonhematopoietic stromal cells in the adipose tissue of WT mice in comparison with cad-11–/– (KO) mice (Supplemental Figure 1; supplemental material available online with this article; https://doi.org/10.1172/JCI86881DS1). Given their spindle shape in ex vivo tissue culture and cell-surface markers, we refer here to CD45–Ter119–CD31–Sca-1+PDGFRα+ cells (nonhematopoietic, non–red blood cells, nonendothelial cells) as adipose tissue fibroblasts. This fibroblast population constitutes over 90% of nonhematopoietic CD45– stromal vascular cells, and it includes fibroblasts, mesenchymal stem cells, adipocyte precursors, and preadipocytes. We detected cell-surface expression of cadherin-11 on approximately 10% to 50% of total adipose tissue fibroblasts (Figure 1A and Supplemental Figure 1). Similarly, we found that cadherin-11 was also highly expressed by a fibroblast population of stromal vascular cells (CD45–CD235a–CD31–) in the omentum of obese humans (Figure 1B). Confocal microscopic analysis further confirmed a typical staining pattern of zipper-like adhesion structures of cadherin-11 at adherens junctions between cells in ex vivo stromal vascular cell cultures (Figure 1C) (32). We further analyzed cadherin-11 expression in epididymal white adipose tissue (eWAT) by quantitative reverse transcription PCR (qPCR) and found that its expression was localized to the SVF, but not to mature adipocytes (Figure 1D). Compared with lean mice fed a normal chow diet (ND), cadherin-11 (Cdh11) mRNA expression tended to be higher in high-fat diet–fed (HFD-fed) WT mice, but did not reach significance (Figure 1E). We found that cell-surface cadherin-11 expression on adipose tissue fibroblasts was similar between lean and obese mice (data not shown). Compared with eWAT, cadherin-11 expression was very low, at or below the level of detection in muscle and liver of HFD-fed WT mice (Figure 1E). These data demonstrate that cadherin-11 is expressed on fibroblast populations but not on mature adipocytes, hematopoietic cells, or endothelial cells in the WAT of mice and humans.

cad-11–/– mice have reduced adipose tissue inflammation and increased M2 macrophages in diet-induced obesity. The appearance of crown-like structures composed of clusters of M1 macrophages and other inflammatory cells is a hallmark of adipose tissue inflammation in obesity. Following HFD feeding, crown-like structures accumulating macrophages were visualized in adipose tissue by immunofluorescence microscopy with staining for CD68+ and by IHC with staining for F4/80. We found that obese cad-11–/– mice had substantially fewer crown-like structures than did obese WT mice (Figure 2A). In contrast to the smaller number of crown-like structures, we detected a higher percentage and number of total macrophages in obese cad11–/– mice (Figure 2, B and C). However, M2 macrophages (CD301+CD11c–F4/80+CD11b+ cells) were the major macrophage population in adipose tissue from both lean and obese cad-11–/– mice. The percentage of M1 macrophages (CD301–CD11c+F4/80+CD11b+ cells) was significantly decreased, but these percentages were similar in adipose tissue of obese cad-11–/– mice compared with that of obese WT mice (Figure 2, B and C). The mRNA expression of M2 macrophage markers such as Arg1, Mrc1, and Il10 was also substantially higher in adipose tissue of obese cad-11–/– mice (Figure 2D). These results indicate that there were increased numbers of M2, but not M1, macrophages in adipose tissue of cad-11–/– mice. Myeloid cell lineage development in bone marrow and monocyte populations (Ly6ChiCXCR3+ and Ly6CloCXCR3+) in peripheral blood appeared normal in the cad-11–/– mice (Supplemental Figure 2, A and B). These results suggested that the increased M2 macrophage numbers in cad-11–/– mice were likely a result of the local adipose tissue microenvironment. Taken together, these findings suggested that cad-11–/– fibroblasts may regulate the adipose tissue macrophage phenotype.

To confirm that fibroblasts in cad-11–/– adipose tissue mediate macrophage differentiation, we prepared cocultures of adipose tissue–derived fibroblasts with BMDMs in vitro. WT and cad-11–/– fibroblasts showed similar effects on the levels of CD206, a M2 macrophage marker expressed in BMDMs (Figure 3B), suggesting that cad-11–/– fibroblasts do not directly produce soluble factor(s) for macrophage polarization into M2 macrophages. However, cad-11–/– fibroblasts significantly enhanced the surface expression of CD206 on BMDMs predifferentiated into M2 macrophages (Figure 3B), which suggested that cad-11–/– fibroblasts promote the M2 macrophage phenotype instead of initiating M2 macrophage polarization.

Next, we examined IL-13 and IL-4, factors that are well known in M2 macrophage differentiation. The levels of both IL-13 and IL-4 were similar in adipose tissue of lean WT and cad-11–/–mice, with a slight trend toward higher Il13 levels in cad-11–/– adipose tissue (Figure 3C). However, Il13 mRNA expression was significantly higher in the adipose tissue of obese cad-11–/– mice compared with mRNA levels in similarly obese WT mice (Figure 3D). Higher IL-13 expression at the protein level was confirmed by ELISA in adipose tissue of obese cad-11–/– mice (Figure 3E). The higher levels of Il13 in cad-11–/– adipose tissue were detected in SVF cells, but not in adipocytes (Figure 3F). These results suggested that higher expression of IL-13 in obese cad-11–/– adipose tissue induces M2 macrophage differentiation.

ILC2s are activated in adipose tissue of obese cad-11–/– mice. Since IL-13 is predominantly produced by ILC2s in adipose tissue (9), we compared ILC2s in adipose tissue of obese WT and cad-11–/– mice (Figure 3G and Supplemental Figure 3A). Indeed, we found that ILC2 numbers were significantly higher in adipose tissue of cad-11–/– mice than in that of WT mice fed a HFD (Figure 3H). Consistent with the lack of expression of cadherin-11 on CD45+ cells shown in Supplemental Figure 1, ILC2s lacked expression of cadherin-11 (data not shown). Furthermore, Il13 expression was markedly higher in flow-sorted ILC2s from adipose tissue of obese cad-11–/– compared with ILC2s from obese WT mice (Figure 3I). This suggests that the expansion and activation of ILC2s are responsible for the increased IL-13 production observed in obese cad-11–/– adipose tissue. Il5 expression by flow-sorted ILC2s was similar in WT and cad-11–/– mice (Figure 3I), which is consistent with there being similar numbers of eosinophils and similar levels of Il4 expression in obese WT and cad-11–/– adipose tissue (Figure 3D and Supplemental Figure 3B). Interestingly, lean cad-11–/– mice had a higher percentage of eosinophils in adipose tissue than did WT mice (Supplemental Figure 3B), which may influence the increased M2 macrophage phenotype in lean cad-11–/– mice. Together, the data suggested that ILC2-derived IL-13 mediates M2 macrophage differentiation in adipose tissue of cad-11–/– mice.

Cad-11–/– fibroblasts produce IL-33 and are expanded in adipose tissue of obese mice. Next, we determined the mechanism by which cad-11–/– fibroblasts mediate ILC2 activation. ILC2s are activated by IL-33, TSLP, and IL-25. Among these, the ST2 ligand IL-33 is known to induce ILC2 expansion in adipose tissue (9, 33). Our qPCR analysis showed that, compared with CD45+ cells, nonhematopoietic cells are the main cells expressing IL-33 (Supplemental Figure 4A). In lean mice, Il33 mRNA appeared slightly higher in the adipose tissue of cad-11–/– mice compared with that of WT mice, but did not reach significance (Supplemental Figure 4B). However, Il33 mRNA and protein expression levels were markedly higher in the adipose tissue of HFD-fed cad-11–/– mice than in that of WT mice (Figure 4A). Further, the levels of Tslp, but not Il25, were also increased in adipose tissue of obese cad-11–/– mice (Supplemental Figure 4C). The increased expression of Il33 was detected in SVF cells, not adipocytes (Figure 4B). qPCR for Il33 in flow-isolated PDGFRα+ fibroblasts revealed that fibroblasts from adipose tissue of obese WT and cad-11–/– mice expressed similar levels of Il33 and other ligands (Figure 4C and Supplemental Figure 4D). To our surprise, however, there was a significant increase in the number of PDGFRα+ fibroblasts in obese cad-11–/– adipose tissue compared with that detected in obese WT mice (Figure 4D and Supplemental Figure 4E). PDGFRα+ fibroblasts were also present at slightly higher levels in adipose tissue of lean cad-11–/– mice (Figure 4D), which was consistent with the slightly higher level of IL-33 expression in adipose tissue of lean cad-11–/– mice compared with that of WT mice (Supplemental Figure 4B). Therefore, we found that the basis for the increased levels of IL-33 resulted not from the amount made per cell in cad-11–/– versus WT fibroblasts, but rather from the significantly higher number of adipose tissue fibroblasts in cad-11–/– mice. We determined whether cad-11–/– PDGFRα+ fibroblasts were increased as a result of a higher proliferation rate. After 5 weeks of HFD feeding, the proliferation rate of cad-11–/– PDGFRα+ fibroblasts (1.992% ± 0.4062%) was significantly lower than that of WT PDGFRα+ fibroblasts (3.528% ± 0.42%) (Supplemental Figure 4F). However, during the first week of the HFD, compared with WT mice (8.014% ± 0.9219%), a significantly higher percentage of PDGFRα+ fibroblasts in adipose tissue of cad-11–/– mice (23.03% ± 3.840 %) consisted of proliferating BrdU+ cells (Figure 4, E and F). These results suggested that the increased number of PDGFRα+ fibroblasts in adipose tissue of cad-11–/– mice results from a higher proliferation rate at the early stage of HFD feeding.

Consistent with these healthy adipocyte functions and insulin sensitivity, we found lower free fatty acids (FFA) and triglycerides (TG) in the serum of HFD-fed cad-11–/– mice (Figure 5H). In addition, livers from obese cad-11–/– mice weighed significantly less (Figure 5I and Supplemental Figure 5E) and had markedly fewer lipid droplets than did livers from obese WT mice (Figure 5J). TLC analyses confirmed that liver TG content was significantly lower in cad-11–/– mice than in WT mice fed a HFD, as quantified by the density of the TLC bands (Figure 5K). Analysis of fatty acid biosynthetic genes in liver showed that mRNA levels of ATP citrate lyase (Acl) and fatty acid synthase (Fasn), but not acetyl-CoA carboxylase 1 (Acc), were decreased in obese cad-11–/– mice (Supplemental Figure 5F). This suggests that de novo lipogenesis was lower and probably contributed to less fat accumulation in the livers of obese cad-11–/– mice. Serum ALT analysis, which measures liver damage (Figure 5L), confirmed that the livers of obese cad-11–/– mice were healthier. In fact, the ALT activity was comparable to that seen in lean WT mice (data not shown). Consistent with improved glucose tolerance, compared with WT mice, we observed significantly improved insulin action in adipose tissue, liver, and muscle of obese cad-11–/– mice, as shown by a greater level of phosphorylated AKT (p-AKT) following insulin administration in vivo (Supplemental Figure 5, G and H). These findings show that cad-11–/– mice have healthy adipose tissue function and markedly less obesity-induced hepatic steatosis and glucose intolerance in diet-induced obesity compared with WT mice.

cad-11–/– mice have significantly less adipose tissue fibrosis. Unresolved chronic inflammation often contributes to tissue fibrosis mediated by fibroblasts and myofibroblasts. Thus, we determined whether cad-11–/– adipose tissue is protected from obesity-induced adipose tissue fibrosis. We found that TGF-β (Tgfb) mRNA expression was markedly lower in obese adipose tissue of cad-11–/– mice than in that of WT mice (Figure 6A), which was consistent with histological analysis of obese adipose tissue that showed significantly less collagen deposition (trichrome-positive blue– or Sirius red–colored areas) in HFD-fed cad-11–/– mice compared with WT mice (Figure 6B and Supplemental Figure 6A). We also found that the expression of several key collagen genes, Col3a1, Col6a2, and Col6a3, was significantly lower in adipose tissue from obese cad-11–/– mice (Figure 6C). To determine whether PDGFRα+ fibroblasts were responsible for the collagen expression in adipose tissue, PDGFRα+ fibroblasts were isolated either by flow cytometry or magnetic beads and found to be the predominant cells producing collagen in adipose tissue. The expression of Col3a1, Col4a1, and Col6a3 was substantially lower in cad-11–/– PDGFRα+ fibroblasts than in WT PDGFRα+ fibroblasts, whereas CD45+ cells showed similar expression levels of these collagens (Figure 6D). In particular, the lower expression levels of Col3a1 and Col6a3 by cad-11–/– PDGFRα+ fibroblasts were consistent with the lower levels of their total mRNA expression in cad-11–/– adipose tissue. These results suggest that both reduced inflammation and lower collagen production by fibroblasts result in less fibrosis in adipose tissue of obese cad-11–/– mice. Interestingly, adipose tissue from obese cad-11–/– mice showed a clearly different morphology from that of obese WT mice (Supplemental Figure 6B). Previous reports have noted that adipocytes can be larger in a flexible and less rigid adipose tissue extracellular matrix (ECM) environment (34, 35). Correspondingly, we found an increased percentage of larger adipocytes in HFD-fed cad-11–/– mice than in WT mice (Figure 6, E and F). Moreover, adipocytes in cad-11–/– adipose tissue expressed healthy adipokines such as FGF21 and adiponectin (Figure 6G). Together, these data suggested that lower collagen production, particularly of COL3 and COL6, prevents adipose tissue fibrosis following HFD feeding in cad-11–/– mice. This likely maintains ECM flexibility and allows adipocytes to grow larger, without the mechanical tension and rupture that contribute to inflammation in obese adipose tissue.

Fibroblasts have been implicated in the regulation of immune responses (26). For example, fibroblastic reticular cells in lymph nodes suppress T cell activation and expansion to maintain peripheral tolerance (21–23). Fibroblasts also modulate inflammation such as that seen with inflammatory arthritis, psoriasis, inflammatory bowel disease, and cancer by recruiting, activating, inhibiting, or maintaining leukocytes in tissues (24, 36, 37). Importantly, inflammation plays a causative role in adipose tissue dysfunction and obesity-induced insulin resistance (1–4, 38, 39). Fibroblast populations including adipocyte precursors are relatively high and account for over 90% of nonhematopoietic stromal vascular cells in adipose tissue. However, the of role stromal fibroblasts in adipose tissue inflammation and diabetes is unknown.

Here, we show that fibroblast function can be modified by either the deficiency or the blockade of mesenchymal cell cadherin-11. By targeting cadherin-11, we found that fibroblasts play a key role in adipose tissue inflammation and glucose intolerance in obesity. Cadherin-11 deficiency strikingly prevented obese mice from adipose tissue inflammation and metabolic syndrome. Adipose tissue inflammation is accompanied by a phenotypic switch from M2 antiinflammatory to M1 proinflammatory macrophages (3, 4, 40). However, despite their obesity, we found that adipose tissue from cad-11–/– mice contained significantly higher numbers of M2 macrophages than did WT mice. We also found that IL-33–mediated ILC2 activation resulted in an increase in IL-13 expression that maintained M2 macrophage phenotypes in adipose tissue of obese cad-11–/– mice.

In obesity, IL-33 plays a protective role in adipose tissue inflammation and insulin resistance (9, 41). IL-33 induces the homeostasis and function of ST2-expressing ILC2s and Tregs (9, 42). However, the source of IL-33 in adipose tissue was unclear. Studies suggested that IL-33 is mainly produced by stromal cells such as epithelial or endothelial cells (43–45). In our study, we found that the levels of IL-33 were much higher in stromal vascular cells than in adipocytes and that IL-33 expression by stromal vascular cells, but not adipocytes, was increased with cadherin-11 deficiency. Furthermore, we found that among SVF cells, PDGFRα+ fibroblasts were the major cells producing IL-33. Some PDGFRα– stromal vascular cells also displayed IL-33 expression, and these stromal vascular cells may include endothelial cells (43) and fibroblasts expressing low levels of surface PDGFRα. Compared with PDGFRα+ fibroblasts, which constitute over 90% of nonhematopoietic cells in SVF cells, the percentage of PDGFRα– stromal vascular cells is much smaller, and thus these cells may not contribute significantly to the production of IL-33 in adipose tissue. IL-33 expression was also detected by immunofluorescence in cadherin-11–expressing cells in adipose tissue of lean mice in a recent study (14), further supporting our finding that PDGFRα+ fibroblasts are the major cells expressing IL-33 in adipose tissue.

A recent report showed that expansion of adipocyte precursor cells occurs within the first week of HFD feeding and that their numbers return to basal levels over the course of a 6-week HFD (46). The rapid proliferation of adipocyte precursors is mediated through activation of the PI3K/AKT2 pathway (46). Interestingly, compared with WT fibroblasts, cad-11–/– fibroblasts showed a markedly higher proliferation rate during the first week of a HFD, with their numbers returning to basal levels by week 5 of the HFD. Data from the Immunological Genome Project (ImmGen) showed that, among PDGF ligands (Pdgfa, Pdgfb, Pdgfc, and Pdgfd), Pdgfc expression is particularly high in adipose tissue macrophages compared with expression levels in macrophages in other tissues. The accumulation of macrophages we observed in cad-11–/– adipose tissue may have provided higher levels of Pdgfc, thereby driving the subsequent proliferation of PDGFRα+ fibroblasts in the adipose tissue of HFD-fed cad-11–/– mice. In addition, we found that the healthy adipocytes in obese cad-11–/– mice allowed adipose tissue to store larger amounts of lipids, which may have reduced obesogenic adipogenesis. Further, we show that the higher IL-33 expression in cad-11–/– adipose tissue resulted from an increase in the number of PDGFRα+ fibroblasts. In turn, IL-33 expression by the expanded PDGFRα+ fibroblasts in cad-11–/– adipose tissue in the first week of the HFD may enhance M2 macrophage differentiation through ILC2-produced IL-13. Therefore, the early response of cad-11–/– mice to a HFD appears to determine the Th2-type antiinflammatory adipose tissue microenvironment, which maintains adipose tissue function and reduces obesity-induced adipose tissue inflammation. Such rapid antiinflammatory mechanisms may also prevent glucose intolerance following binge eating by animals such as predators in the wild as well as in humans experiencing overnutrition.

Obesity-induced adipocyte hypertrophy and hyperplasia require extensive adipose tissue remodeling. ECM proteins and their turnover are essential for both the development and remodeling of adipose tissue (34, 35). Less rigid ECM in WAT better accommodates adipocyte enlargement, with less adipocyte death and inflammation in obesity (16, 34). Fibrosis contributes to adipose tissue dysfunction and has a causative role in insulin resistance in obesity (1, 16, 39, 47, 48). A recent study showed that COL6-deficient mice had less adipocyte death and adipose tissue fibrosis, which were associated with improved glucose metabolism in both HFD-induced and genetically obese mice (34). Importantly, we found that cadherin-11 deficiency reduced the production of collagens COL3 and COL6 by fibroblasts and resulted in substantially less adipose tissue fibrosis in obesity. Anti–cadherin-11 mAb blockade also markedly reduced COL6a3 production. These data suggest that cadherin-11 regulates collagen production by adipose tissue fibroblasts, and this may help to preserve adipose tissue flexibility, larger adipocytes, and reduced adipocyte necrosis and inflammation crown-like structures in obese cad-11–/– mice. In addition, cadherin-11 blockade may be relevant to other diseases linked by ECM deposition by cadherin-11–expressing fibroblasts or myofibroblasts. A recent study showed that obesity increases myofibroblasts and ECM stiffness in the adipose tissue of mammary fat and that changes in ECM mechanics promote breast tumorigenesis in obesity (49). It would be interesting to determine whether blocking cadherin-11 in the myofibroblasts of mammary fat can reduce the risk for breast tumorigenesis by inhibiting obesity-induced collagen production.

In summary, cad-11–/– mice are protected from obesity-induced glucose intolerance and fatty liver as a result of reduced adipose tissue inflammation associated with the axis of stromal cell IL-33, ILC2s, and M2 macrophages, as well as less adipose tissue fibrosis. Fibroblast stromal cells expressing cadherin-11 play a major role in regulating the activation of innate immune cells and adipose tissue matrix stiffness. These findings strongly point to the importance of mesenchymal stromal cells and the opportunity to target them via cadherin-11 in the management of adipose tissue inflammation, diabetes, and metabolic syndrome.

Animal studies. The cad-11–/– mice and control B6:129 F1–intercrossed mice were maintained at Taconic. Littermates of WT and cad-11–/– mice were bred and maintained at Taconic. WT C57BL/6 mice were purchased from Taconic. When needed, mice were shipped to the Dana-Farber mouse facility and maintained in the same room during the experiments. Male mice, 6 to 8 weeks of age, were given a HFD, which consisted of 60% kcal from fat (D12492; Research Diets), or a ND (ProLab IsoPro RMH 3000; LabDiet) for 5 to 12 weeks as indicated in each figure legend. For GTTs, mice were fasted for 6 hours or overnight for 10 hours and given i.p. D-glucose (1 g glucose per 1 kg BW). Blood glucose levels were determined at 0, 15, 30, 60, and 90 minutes after glucose injection using the OneTouch Ultra Glucometer (LifeScan Inc.). ITTs were performed after a 4-hour morning fast and i.p. injection of insulin (0.75 IU/kg BW) (HumilinR 100 U/ml; Eli Lilly). Blood glucose levels were measured at 0, 15, 30, 60, and 90 minutes. The HOMA-IR index was calculated as follows: insulin (μIU/ml) × glucose (mg/dl)/405. For Ab treatment experiments, B6 mice were fed a HFD for 6 weeks. mIgG1 isotype control Ab or anti–cadherin-11–specific mAb (SYN12) was given i.p. to HFD-fed mice at 10 mg/kg BW every 3 days for 3 weeks. For the Ab experiments in Supplemental Figure 3, Ab treatment was initiated on B6 mice fed a HFD for 3 weeks. mIgG1 or anti–cadherin-11 mAb (SYN12) was given i.p. at 500 μg per mouse for the first dose and then at 100 μg per mouse every 3 days for 2 weeks. Body composition was analyzed in conscious mice using an EchoMRI 3-in-1 analyzer.

Adipose tissue digestion. Adipose tissue was cut into small pieces and digested by enzyme mixture (RPMI 1640 medium containing 1 mg/ml collagenase type 2 [LS004188; Worthington Biochemical]; 0.1 mg/ml DNase I [10104159001; Roche]; and 0.8 mg/ml Dispase II [04942078001; Roche]) for 1 hour at 37°C. During digestion, released cells were collected on ice, and fresh enzyme mixture was added every 10 minutes. Using this method, adipose tissue was completely digested to release stromal cells including fibroblasts. Released cells were spun down to separate SVF cells from floating adipocytes. Stromal vascular cells were resuspended in complete RPMI 1640 medium containing 10% FBS and filtered through a 70-μm filter. Total live cell numbers in the SVF were counted using a trypan blue exclusion test.

Flow cytometric analysis. Cells were incubated with Zombie Aqua (1:100; BioLegend) in PBS at room temperature for 5 minutes. After washing, cells were resuspended in FACS buffer (2 % FBS, 2 mM EDTA, 0.05 % NaN3 in PBS) and incubated with anti-CD16/32 Abs in FACS buffer for 10 minutes on ice, followed by staining with the Abs indicated in figures in FACS buffer for 15 minutes at 4°C. After washing, the stained cells were analyzed using a FACSCanto II System (BD Biosciences). Data were analyzed with FlowJo and FCS Express 5 (De Novo Software) software. For cadherin-11 detection, stromal vascular cells were stained with Zombie Aqua as described above, except 2 mM CaCl2 in HEPES-buffered saline (HBS-Ca++) was used instead of PBS. After washing, Fc receptors were blocked with anti-CD16/32 Abs and then incubated with biotinylated anti–cadherin-11 Ab (0.5 μg) for 20 minutes on ice in HBS buffer (2 % FBS in HBS-Ca++) to minimize cadherin proteolysis. After washing, the cells were stained with APC-conjugated streptavidin and other fluorescence-labeled Abs against surface markers (Ter119, CD45, CD31, Sca-1, and PDGFRα). Cadherin-11 expression was analyzed on hematopoietic cells (CD45+Ter119–) and fibroblast stromal cells (CD45–Ter119–CD31–Sca-1+PDGFRα+) after excluding dead cells and doublets.

Immunofluorescence. For whole fat tissue staining, 5 mm2 of tissue was fixed in 4% paraformaldehyde in PBS overnight, washed in PBS for 2 days at 4°C, and permeabilized and blocked in blocking buffer (5% serum, 1% BSA, and 1%Triton X-100 in PBS) overnight at 4°C. Then, tissues were stained with the indicated Ab below in blocking buffer for 2 days and washed in blocking buffer for 1 day at 4°C, followed by staining with Alexa Fluor 488–conjugated goat anti-mouse CD68, Alexa Fluor 568 phalloidin (F-actin), and DRAQ5 (nucleus) in blocking buffer overnight at 4°C. After washing tissue pieces for 3 days at 4°C, images were taken by confocal microscopy (TE2000-U; Nikon). For cadherin-11 detection in ex vivo stromal vascular cell cultures, freshly released SVF cells were seeded on a glass coverslip in DMEM medium containing 10% FBS, 2 mM L-glutamine, 100 units/ml penicillin, 100 μg/ml streptomycin sulfate, 10 μg/ml gentamycin, and 55 μM 2-mercaptoethanol (Gibco-BRL, Thermo Fisher Scientific) at 37 °C under 10% CO2. After 2 days of culture, cells were fixed in 4% paraformaldehyde in HBS-Ca++ for 20 minutes at room temperature and washed 4 times for 5 minutes each. Cells were then permeabilized in 0.2% Triton X-100 in HBS-Ca++ for 3 minutes and then washed twice for 5 minutes each. After treatment with blocking buffer (HBS-Ca++ containing 1% BSA and 10% FBS) for 1 hour at room temperature, cells were incubated with anti–cadherin-11 Ab (1:500; 3H10, in-house) in blocking buffer overnight at 4°C. After dip-washing 6 times, cells were stained with Alexa Fluor 488–conjugated goat anti-mouse Ab (1:750); Alexa Fluor 568 phalloidin (1:500); and DRAQ5 (1:500) for 1 hour at room temperature. Cells were washed twice with blocking buffer and twice with HBS-Ca++ for 5 minutes each. Images were taken by confocal microscopy.

Statistics. All data are presented as the mean ± SEM. Statistical significance was determined using a Student’s 2-tailed t test or 2-way ANOVA. A P value of less than 0.05 was considered statistically significant. GraphPad Prism 5 (GraphPad Software) was used for all statistical analyses.

Study approval. Animal studies were approved by the Dana-Farber Cancer Institute animal care and use committee. Discarded visceral adipose tissues from obese patients were obtained with IRB approval of Brigham and Women’s Hospital.

SKC and MBB conceived and designed the experiments and wrote the manuscript. SKC, ACK, BJW, FM, KW, PYL, DD, LL, and VCM performed the experiments. XM performed and analyzed the confocal images. ASB critically reviewed the manuscript.

Conflict of interest: M.B. Brenner is a consultant for Roche, and M.B. Brenner, S.K. Chang, and L. Lynch have filed a patent describing targeting cadherin-11 as a new approach for treating type 2 diabetes and metabolic syndrome (US provisional application No. 62/091,709 and international patent PCT/US2015/065751).

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